It means that the incoming supply wires must be rated for 90ºC (194ºF). If the wire was installed around 1985 or later, don't worry about it.

If the wire is older, it *might* be rated for 60ºC or less. This rating applies to the insulation on the wires; above the rated temperature the insulation can begin to degrade. The wires may be heated not from load, but from the heat from the light bulbs. If you install larger incandescent bulbs than the labeling indicates, you can overheat the wires.

(By the way, the watt rating is actual wattage. For example, if it says 60 watts, that's 60 watts incandescent. A "60 watt equivalent" CFL is only 13 actual watts -- you could safely install a "100 watt equivalent" CFL if you wanted to.)

If the insulation on the wires at all seems brittle, it has gotten too hot in the past and may indicate a dangerous situation.

Thanks for this information. It is very helpful. I need to install a motion detector and there are 2 ground wires coming from the 2 different light bulbs. Are they attached to grounding screw in the box or is it attached to grounding
screw in the fixture?
Thanks for helping.

All ground wires should be connected together with a wire nut. You'll also need short jumpers from any ground screws to this same connection. Yes, this can result in a LOT of wires in one wire nut; if you don't have a big enough wire nut, you can use two wire nuts, jumpering between them. Or use a crimp-on sleeve connector.

Hi again,
I would like to know if the electrical box is grounded, what do I do with copper wires coming from light fixture?
With box grounded I believe it has protection I need? Also the light fixture requires 2-150 watt halogen lights.
Could it overheat wires as you have explained?
Thanks

If the box is grounded (as it would likely be if your wiring is in conduit), you can attach a jumper wire to a screw in the back of the box. Many boxes have a hole tapped for a #10-32 machine screw for this purpose. Connect that jumper wire to the wire from the fixture.